Field of the Invention
This invention relates to processes and systems for production of asphalt and desulfurized and deasphalted oil.
Description of Related Art
Crude oils contain heteroatoms such as sulfur, nitrogen, nickel, vanadium and others in quantities that impact the refinery processing of the crude oils fractions. Light crude oils or condensates contain sulfur as low as 0.01 weight % (W %), in contrast, heavy crude oils contain as high as 5-6 W %. Similarly, the nitrogen content of crude oils is in the range 0.001-1.0 W %. The heteroatom contents of various Saudi Arabian crude oils are given in Table 1. As seen, the heteroatom content of the crude oils within the same family increases with decreasing API gravity on increasing heaviness. The heteroatom content of the crude oil fractions also increases with increasing boiling point (Table 2).
TABLE 1PropertyASLAELALAMAHGravity, °51.439.533.031.127.6Sulfur, W %0.051.071.832.422.94Nitrogen, ppmw70446106414171651RCR, W %0.511.723.875.277.62Ni + V, ppmw<0.12.92134.067ASL—Arab Super LightAEL—Arab Extra LightAL—Arab LightAM—Arab MediumAH—Arab Heavy
TABLE 2Fractions, ° C.Sulfur W %Nitrogen ppmwC5-900.01 93-1600.03160-2040.06204-2600.34260-3151.11315-3702.00253370-4302.06412430-4822.65848482-5703.091337
Contaminants (poisonous compounds) such as sulfur, nitrogen, poly-nuclear aromatics in the crude oil fractions impact the downstream processes including hydrotreating, hydrocracking and fluid catalytic cracking (FCC). The contaminants are present in the crude oil fractions in varying structures and concentrations. These impurities must be removed during the refining to meet the environmental regulations for the final products (e.g., gasoline, diesel, fuel oil) or for the intermediate refining streams that need to be processed for further upgrading such as reforming isomerization.
In conventional refining schemes, crude oil is first distilled in an atmospheric column to separate sour gas and light hydrocarbons including methane, ethane, propane, butanes and hydrogen sulfide, naphtha (36-180° C.), kerosene (180-240° C.), gas oil (240-370° C.) and atmospheric residue bottoms which include hydrocarbons boiling above 370° C.
The atmospheric residue from the atmospheric distillation column is either used as fuel oil or sent to a vacuum distillation unit, depending on the configuration of the refinery. In configurations in which the bottoms are further distilled in a vacuum distillation column, products obtained include vacuum gas oil having hydrocarbons boiling in the range 370-520° C. and vacuum residue having hydrocarbons boiling above 520° C.
As the boiling point of the petroleum fractions increases, the quality of oil decreases and negatively impacts the downstream proceeding units. Table 3 and Table 4 provide quality of atmospheric (boiling above 370° C.) and vacuum residual (boiling above 520° C.) oils derived from various crude sources. It is clearly shown in these tables that the atmospheric or vacuum residues are highly contaminated with heteroatoms and have high carbon content and the quality deteriorates with increasing boiling point.
TABLE 3APISulfur,NI + V,CCR,sourcenameGravity, °W %ppmwW %Middle EastArabian Light16.803.14550.007.60Middle EastArabian Heavy12.704.30125.0013.20South AsiaMina26.400.1516.004.20South AsiaDuri17.500.2217.009.30ChinaShengli18.701.2319.008.60ChinaTaching25.100.134.004.00Latin AmericaMaya8.304.82494.0017.40Latin AmericaIsthmus13.902.9653.008.20
TABLE 4APISulfur,Ni + V,CCR,sourcenameGravity, °W %ppmwW %Middle EastArabian Light6.904.34141.0020.30Middle EastArabian Heavy3.006.00269.0027.70South AsiaMina17.300.1944.0010.40South AsiaDuri13.000.2532.0015.20ChinaShengli11.701.6628.0016.40ChinaTaching18.700.189.009.50Latin AmericaMaya−0.105.98835.0029.60Latin AmericaIsthmus4.004.09143.0021.10
Naphtha, kerosene and gas oil streams from crude oils or other natural sources such as shale oils, bitumens and tar sands, are treated to remove the contaminants mainly sulfur, whose quantity exceeds the specifications. Hydrotreating is the most common refining technology to remove these contaminants (poisonous compounds for other processes/catalysts). Vacuum gas oil is processed in a hydrocracking unit to produce gasoline and diesel or in an FCC unit to produce mainly gasoline, and LCO and HCO as by-products. The former of which is either used as a blending component in a diesel pool or fuel oil, while the latter is sent directly to the fuel oil pool. There are several processing options for the vacuum residue fraction, including hydroprocessing, coking, visbreaking, gasification and solvent deasphalting.
In additional configurations, vacuum residue can be treated in an asphalt unit to produce asphalt by air oxidation. Asphalt oxidation is a process in which air is bubbled through the feedstock or pitch in an oxidizer column vessel to oxidize sulfur-containing compounds. It is a non-catalytic process to shift the sulfur molecules from the oil phase to the asphalt phase.
As noted above, in some refining configurations, the vacuum residue can be processed in a solvent deasphalting unit to separate the solvent soluble (deasphalted oil) and insoluble oil (asphaltenes) fractions.
Solvent deasphalting is an asphalt separation process in which residue is separated by polarity, instead of by boiling point, as in the vacuum distillation process. The solvent deasphalting process produces a low contaminant deasphalted oil (DAO) rich in paraffinic type molecules. These fractions can then be further processed in conventional conversion units such as an FCC unit or hydrocracking unit. The solvent deasphalting process is usually carried out with paraffin C3-C7 solvents at or below critical conditions.
Further material regarding solvent deasphalting can be found in U.S. Pat. Nos. 4,816,140; 4,810,367; 4,747,936; 4,572,781; 4,502,944; 4,411,790; 4,239,616; 4,305,814; 4,290,880; 4,482,453 and 4,663,028, all of which are incorporated herein by reference.
While individual and discrete asphalt oxidation and solvent deasphalting processes are well developed and suitable for their intended purposes, there remains a need in the art for more economical and efficient processes for obtaining product from heavy fractions such as atmospheric residues.